Solid propellant



Oct. 26, 1965 BOWMAN E 3,214,305

SOLID PROPELLANT Filed June 4, 1952 INVENTORS. Norman J. Bowman y Wayne A. Proell ATQORNEY United States Patent 3,214,305 SOLID PROPELLANT Norman J. Bowman, Hammond, Ind., and Wayne A.

Proell, Chicago, Ill., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed June 4, 1952, Ser. No. 291,754 11 Claims. (Cl. 149-19) This invention relates to a composition for the generation of gas, which composition can be used as an explosive. More particularly, the invention relates to explosive compositions wherein ammonium nitrate is substantially the only explosive agent. Still more particularly, the invention relates to a shaped composition for the generation of gas by the decomposition of a mixture comprising essentially ammonium nitrate, oxygenated oxidizable material and a catalyst. Also, the invention relates to a novel composition usable as a binder for a shaped explosive. Further, the invention relates to methods for the preparation of said binder and said shaped explosive composition. Also, the invention relates to a method of propelling rockets or assisting in the propulsion of aircraft.

Ammonium nitrate is widely used as a component of high explosives, particularly the so-called safe explosives. Even though ammonium nitrate is classified as a high explosive, it is extremely insensitive to ordinary heating and to shock and cannot readily be detonated by the local application of heat or by a blasting cap. Further, when ignited, ammonium nitrate alone does not burn uniformly and has a tendency to go out. In order to improve the burning quality to increase the sensitivity and to utilize the excess free-oxygen available from the decomposition of the ammonium nitrate, oxidizable materials, such as, carbon, cellulosic materials, hydrocarbons, etc. are admixed with the ammonium nitrate.

World War II utilized in tremendous quantity rockets for ground-to-ground missiles, ship-to-shore missiles, airto-ground and air-to-air missiles. These rockets comprised essentially a thin-walled casing which contained a combustion chamber containing a quantity of solid propellant, a nozzle through which the decomposition gases passed and created the forward thrust, stabilizing fins and a war head which contained the explosive. The military rockets utilized the so-called double base powders such as Ballistite as the solid propellant. Also, there was developed the use of rocket units to assist in the take-off of either heavily ladened airplanes or to overcome a short runway. These units are commonly known as JATO (jet assisted take-off) or ATO (assisted takeoff) units.

The use of ammonium nitrate-base compositions as solid propellants for rockets and ATO units is quite attractive because of the cheapness and availability of ammonium nitrate; because of the relatively low flame temperature of the decomposition of ammonium nitrate, between about 3150 and 3900 F. (1730-2150 C); and because the excess free-oxygen available from the decomposition permits the use of oxidizable material to improve the energy obtainable from the decomposition. However, it was found that the physical characteristics of ammonium nitrate seriously interfered with the development of ammonium nitrate-base solid propellants.

Solid ammonium nitrate can exist in five different forms. These forms are stable in certain temperature ranges and pass readily into the form stable at a diiferent range when the temperature of the solid is brought to the transition temperature or a degree or two beyond the transition temperature. Each phase change is accom panied by a change in the volume occupied by a unit weight of the ammonium nitrate. There are given below data on the transition temperatures of the various known solid forms of ammonium nitrate and also the approximate volume change in terms of percent.

Temperature 1 Volume Phase Change 1 Change Percent 2 0 F 1 R. G. Early-T. M. Lowry, J. Chem. Soc. 115, 1187 (1919).

2 International Critical Tables.

It is obvious from the above that an ammonium nitratebase composition would be seriously affected by storage at ordinary atmospheric temperatures since large volume changes occur at about 0 F. and about R, which temperatures occur very commonly.

Therequirement for a solid propellant that is suitable for military use is that it be ballistically stable after prolonged storage at temperatures between about to -65 F. (+74 to -54 C.). Many binders have been used to form a shaped solid propellant (grain). However, no successful ammonium nitrate-base grain has been developed by other workers in this art. Binders which produced a grain that resisted the formation of cracks (fissures) were sufficiently thermoplastic that the grain flowed at higher atmospheric temperatures and became deformed. A deformed grain cannot be used because its ballistic characteristics are not predictable. Other binders which give grains that were dimensionally stable at these temperatures were unable to withstand the volume change occurring during the transformation of the ammonium nitrate from one form to another; these grains developed fissures both entirely internal and/or extending to the surface of the grain. These fissures act as burning surfaces and change the burning characteristics of the grain, thus making the ballistic performance of the rocket or ATO unit unpredictable. These difficulties with ammonium nitrate have resulted in the use of double base powders for military rockets and mixtures of special asphalts and ammonium perchlorate for ATO units.

An object of this invention is the preparation of a gas generating composition using ammonium nitrate as the principal gas generating material. Another object is the prepaartion of a shaped explosive composition (grain) comprising essentially ammonium nitrate, an oxygenated binder and a combustion catalyst, which grain is dimensionally stable and non-fissuring in the range between about 165 and -65 F. Still another object is a gas generating composition comprising ammonium nitrate, an oxygenated binder and a combustion catalyst which is suitable for use in rockets and ATO units. Yet another object is the preparation of a composition which is suitable for use as a binder for a mixture of ammonium nitrate and a combustion catalyst. A further object of this invention is a method for the preparation of said binder. A particular object is a method for the manufacture of a shaped explosive composition which is suit able for use in rockets and ATO units. Still another object is a method of propelling rockets and assisting in the propulsion of aircraft.

FIGURE 1 is a longitudinal view of an ATO unit.

FIGURE 2 is a crosssectional view of said ATO unit taken along the line 22.

The above objects and other objects which will become apparent in the course of the detailed description have been achieved as follows. The explosive composition of this invention comprises essentially:

(1) At least about 70 weight percent of ammonium nitrate,

(2) An effective amount of a combustion catalyst, and (3) Between about 18 and 29 weight percent of a binder, which binder comprises essentially (A) Between about 18 and 40 weight percent of cellulose acetate which analyzes between about 51 and 57 weight percent of acetic acid; (B) Between about and 60 weight percent of the reaction product of (i) At least one dihydric alcohol selected from the class consisting of ethylene glycol, polyethylene glycol, propylene glycol, poly propylene glycol,- n-butylene glycol and poly n-butylerie glycol, which polyglycols have a molecular weight of less than about 400, and

(ii) At least one acid selected from the class consisting of aliphatic dicarboxylic acids and aliphatic oxydicarboxylic acids, which acids contain between 2 and 6 carbon atoms, and wherein the mol ratio of said alcohol to said acid is between about 1.02 and 1.3; and

(C) Between about 20 and 60 weight percent of a modifier selected from the class consisting of mononitrodiphenyl, dinitrodiphenyl, mixtures of mononitrodiphenyl and dinitrodiphenyl, mixtures of the foregoing with trinitrodiphenyl, mononitrodiphenyl oxide, dinitrodiphenyl oxide, mixtures of mononitrodiphenyl oxide and dinitrodiphenyl oxide and mixtures of the foregoing oxides Wlthg trinitrodiphenyl oxide, in which trinitro compound-containing mixtures there is an average of less than about 2.5 nitro groups per molecule and essentially not more than two nitro groups are present on any benzene nucleus.

The term ammonium nitrate as used in this specification and in the claims is intended to mean either ordinary commercial grade ammonium nitrate, such as, conventionally' grained ammonium nitrate containing a small amount of impurities and which is then generally coated with a small amount of moisture-resisting material such as petroleum or paratfin, or military grade ammonium nitrate, or a mixture of minor amounts of other inorganic nitrates and ammonium; nitrate. V

Finely powdered ammonium nitrate contains about 20 volume percent of void space. This void space must be completely filled in order to obtain a shaped explosive grain of the desired physical characteristics. When the combustion catalyst is an organic material, some of the void space is filled by the catalyst. However, when using an inorganic compound as the catalyst, the binder must not only fill the voids of the ammonium nitrate, but also the voids presentin the finely powdered inorganic material catalyst. In order to avoid soot formation which leads to a smoky exhaust, it is desirable to have the explosive composition approximately in stoichiometric balance with respect to oxygen content. When using binders that have a high oxygen demand, i.e., are low in bound oxygen content such as hydrocarbons, it has been found that grains approaching the desired characteristics are badly out of oxygen balance. Some lack of oxygen balance due to excess of oxidizable materials is tolerable even though the unbalanced composition has a lower thrust than does the composition that is approximately in oxygen balance. It has been discovered that by the use of oxygenated oxidizable materials as binders [for the ammonium nitrate-base composition, it is possible to attain the desired physical characteristics and also to attain approximate oxygen balance.

The composition of matter used as the binder in the explosive composition of this invention comprises essentially three components. These components are a polymer, a plasticizer and a modifier. The polymer imparts strength, tear resistance and rigidity to the binder and to the explosive grain. It has been discovered that a particular group in the generic material commonly known as cellulose acetate possesses the necessary properties for the polymer. The cellulose acetate used as the polymer in this invention is known as a partially esterified cellulose acetate and is described as having an acetic acid content between about 51 and 57 weight percent. The term weight percent acetic acid denotes the amount of acetic acid obtained on saponification of the cellulose acetate and is expressed as percent of the initial material. A particularly suitable cellulose acetate is one which analyzes between about 54 and 56 weight percent of acetic acid. Particularly good results are obtained when using the commercial grade of cellulose acetate known as lacquer grade. Lacquer grade cellulose acetate is described in addition to its acetic acid content by its viscosity, when dissolved in acetone, of between about 2 and centipoises at 25 C. Hereinafter the term viscosity as applied to cellulose acetate denotes the viscosity of an acetone solution containing 20 weight percent of the cellulose. The preferred cellulose acetate of this invention analyzes between about 54 and 56 weight percent acetic acid and has a viscosity of between about 2 and 10 centipoises. A binder having the proper characteristics for use in preparing the shaped explosive composition of this invention contains between about 18 and 40 weight percent of the defined cellulose acetate. Pref= erably, the binder contains between about 18 and 25% of the defined cellulose acetate.

The plasticizer utilized in the binder of this invention consists essentially of the product of the polyesterification reaction of a dihydric alcohol and a dicarboxylic acid wherein a molar excess of alcohol is used. In order to obtain a plasticizer of the desired thermoplastic characteristics and having the proper solvent action on the polymer, it is necessary to use a dihydric alcohol wherein the hydroxyl groups are the only functional groups and a dicarboxylic acid wherein the carboxylic groups are the only functional groups, i.e., a polyester having substantially no cross linkages is desired.

It has been discovered that the dihydric alcohol used in the preparation of the plasticizer must be selected from at least one of the dihydric alcohols in the class consisting of ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, n-butylene glycol and poly n-butylene glycol; the polyglycols must have a molecular weight of less than about 400 in order to produce a polyester of the desired properties.

The dicarboxylic acids utilized in the preparation of the plasticizer must be selected from at least one member of the class consisting of aliphatic dicarboxylic acids and aliphatic oxydicarboxylic acids, which acids have between 2 and 6 carbon atoms in the molecule. Examples of the dicarboxylic acids are malonic acid, succinic acid, glutaric acid and adipic acid. Examples of the oxydicarboxylic acids are diglycolic acid (oc,oc' oxydiacetic acid), oxyaceticapropanoic acid and oxydipropan-oic acid. It is preferred to use the oxydicarboxylic acids because of their favorable effect on the oxygen demand of the binder.

It has been discovered that the molecular weight of the product of the polyesterification reaction has a considerable effect on the plasticizing properties of the product. A low molecular weight is desirable and this desired molecular weight is obtained by using a molar excess of alcohol over acid. The mol ratio of alcohol to acid should be between about 1.02 and 1.3, preferably between about 1.15 and 1.25.

The plasticizer of this invention may be prepared by any of the conventional methods known to the art, e.g., the desired amounts of alcohol and acid are charged to a heated reaction zone wherein the temperature of the materials is maintained at about C. The waterevolved in the reaction is withdrawn from the reaction Zone by means of a condenser which refluxes back to the reaction zone any glycol and acid which may have vaporized. Preferably, the reaction zone is operated under vacuum. The reaction is continued until the evolution of water has substantially ended. The contents of the reaction zone, hereinafter known as reaction product of the polyesterification reaction, are cooled and sent to storage for future use in the preparation of the binder of this invention.

The binder of this invention contains between about 20 and 60 weight percent of the polyesterification reaction product and preferably between about 25 and 45 weight percent.

The modifier utilized in the preparation of the binder of this invention is selected from the class consisting of mononitrodiphenyl, dinitrodiphenyl, mixtures of mononitrodiphenyl and dinitrodiphenyl, mixtures of the foregoing with trinitrodiphenyl, mononitrodiphenyl oxide, dinitrodiphenyl oxide, mixtures of mononitrodiphenyl oxide and dinitrodiphenyl oxide and mixtures of the foregoing oxides with trinitrodiphenyl oxide, in which trinitro compound-containing mixtures there is an average of less than about 2.5 nitro groups per molecule and essentially not more than two nitro groups are present on any benzene nucleus. The combination of cellulose acetate and polyester does not possess suitable characteristics for the preparation of a satisfactory explosive grain. It has been found that some modifying material must be added to improve the rigidity of the plasticized polymer without adversely affecting the thermoplastic characteristics of the plasticized polymer and also without seriously affecting the oxygen demand of the binder. It has been discovered that nitrodiphenyls and nitrodiphenyl oxides such as are obtained by the nitration of diphenyl and diphenyl oxide are suitable modifiers. It has further been discovered that trinitrodiphenyls and trinitrodiphenyl oxides are not suitable modifiers because of low compatibility with the plasticized polymer. However, mixtures of nitrodiphenyls and nitrodiphenyl oxides which contain an average of less than about 2.5 nitro groups per molecule are suitable modifiers for the purposes of this invention. This average nitro content may be attained with mixtures of mononitrodiphenyl (oxide) and trinitrodiphenyl (oxide), dinitrodiphenyl (oxide) and trinitrodiphenyl (oxide), or mixtures of all three nitro compounds. It is preferred to use the dinitrodiphenyls (oxides) and in particular the 2,4-dinitrodiphenyl oxide.

The trinitro derivatives wherein all three nitro groups are present on one benzene nucleus in the molecule are sensitive and tend to explode violently on heating to elevated temperatures. However, very slight amounts of these isomers can be present without rendering the particular nitrodiphenyl (oxide) unusable for the purposes of this invention. Normally the trinitro derivative containing mixtures will contain less than about 1 or 2% of the undesired isomer which contains three nitro groups on a single benzene nucleus.

The binder of this invention contains between about 20 and 60 weight percent of the defined nitro derivatives, and preferably between about 25 and 45 weight percent.

To recapitulate: The composition of matter that is used as a binder for the ammonium nitrate base-explosive of this invention comprises essentially between about 18 and 40 weight percent of a defined cellulose acetate polymer, between about 20 and 60 weight percent of a de fined plasticizer and between about 20 and 60 weight percent of a defined modifier. Preferably, the binder comprises essentially between about 18 and 25 weight percent of polymer, between about 25 and 45 weight percent of plasticizer and between about 25 and 45 weight percent of modifier. It is preferred that the plasticizer and nfdt'fifier be present in about the same amounts on a weight basis, i.e., in about equal quantities.

The binder of this invention is preferably prepared by heating the plasticizer to a temperature between about 100 and 150 C. and adding to the hot plasticizer the desired amount of modifier. The mixture is agitated while being maintained at the elevated temperature above the melting point of the modifier and the agitation is continued until a substantially homogeneous mixture has been attained. The mixture of the plasticizer and the modifier is maintained above the melting point of the modifier while the desired amount of polymer is added thereto, A suitable temperature is between about and C. The three-component mixture is agitated while being maintained at the elevated temperature until a smooth homogeneous plastic mass is obtained. When cooled to ambient temperature the binder is a hard, tough material which has thermoplastic properties. .The binder is readily converted to a viscous liquid by heating to a temperature above about 90 C. While the order of polymer and modifier addition need not be as above, the blending process is simplified by the order given.

A mixture of ammonium nitrate and defined binder is quite insensitive and extremely difficult to ignite at ambient temperatures and pressures. An effective amount of a combustion catalyst must be present in order to obtain a readily ignitable and uniform burning explosive composition.

It is well known in this art that the addition of certain types of organic materials will improve the sensitivity of ammonium nitrate. Examples of materials which may be added to improve sensitivity are nitrostarch, nitro cellulose and nitroglycerine. However, only small amounts of these materials can be tolerated without making the composition too sensitive for use as a solid propellant. Materials such as wood flour and sucrose improve the sensitivity of ammonium nitrate-base explosives. Nitrogen containing organic compounds are particularly good for use as combustion catalysts when they do not unduly sensitize the composition. Examples of suitable materials are urea, nitroguanidine, guanidine nitrate and mononitrate naphthalene. The element sulfur is an effective sensitizer for the ignition of ammonium nitrate. A particularly effective catalyst for the ignition of ammonium nitrate-oxidizable material mixtures is the element carbon when present in amounts of 6 weight percent or more. The amount of organic combustion catalyst needed to render the composition readily ignitable and to produce a uniform rate of combustion varies with the particular type of catalyst material added. While at least an effective amount must be present, it is preferred to keep the amount of organic combustion catalyst at a minimum in order to obtain a grain of proper balance with regard to stoichiometry and strength.

The most commonly used method for improving the sensitivity of ammonium nitrate-base explosives is to add a chromium containing combustion catalyst. The chromium containing combustion catalysts are ammonium chromate, ammonium polychromate, alkali-metal chromate, alkalimetal polychromate, chromic oxide, chromic nitrate and copper chromite. The preferred commercial catalyst is ammonium dichromate. The chromium-type catalysts are extremely effective but have the disadvantage of being expensive and of frequently being virtually unobtainable; furthermore, the chromates are relatively hazardous to handle without the use of special precautions. A more serious disadvantage for military use is the fact that on prolonged storage at somewhat elevated temperatures the chromates tend to react with the oxidizable material in the composition to give chromate salts which are not as effective catalytically as ammonium dichromate. The amount of chromium-type catalyst that must be present in the shaped explosive composition of this invention is between about 1 and 8 weight percent and preferably between about 2 and 4 weight percent.

In addition to the above described inorganic chromiumtype catalyst, it has been found that certain organiochromium compounds are effective as catalysts. These compounds are disclosed in US. patent application Serial Number 279,968, now Patent No. 2,997,377, filed April 1, 1952, by Wayne A. Proell. These organo-chromium compounds are selected from the chromate salts of the class consisting of aliphatic polyamines, cycloaliphatic polyamines and alicyclic secondary amines. Examples of these compounds are ethylene diamine chromate, 'triethylene tetramine chromate, hexamethylene diamine chromate, piperidine chromate and dimethyl piperazine chromate.

It has been discovered that certain iron compounds are effective catalysts for the combustion of ammonium nitrate and ammonium nitrate-oxidizable material mixtures. These catalysts are the subject matter of US. patent ap plications filed by Wayne A. Proell and William G. Stanley, Serial Number 273,564, now abandoned, filed February 26, 1952, and Serial Number 288,065, filed May 15, 1952, now Patent No. 2,955,033. All of the combustion catalysts disclosed in these applications contain the iron cyanide radical, either ferrocyanide or ferricyanide. In addition to the iron cyanide radical, these catalysts contain a second iron ion which may be either ferric or ferro (us). In addition to the iron-iron cyanide complex, the catalyst may contain alkali metal and/or ammonium ions. It has been found that the generic classes of iron-iron cyanide compounds known as soluble Prussian blues and insoluble Prussion blues are effective catalysts for the purposes of this invention. It is known that the better soluble Prussian blues contain alkali metal such as potassium and sodium and/ or the ammonium radical. Some of the compounds which have been found to be effective are: ferro ferrocyanide, ferric ferrocyanide, ferro ferricyanide, ferric ferricyanide, potassium ferric ferrocyanide, sodium ferric ferrocyanide, ammonium ferric ferrocyanide, potassium soluble Prussian blue, sodium soluble Prussian blue and ammoniumsodium soluble Prussian blue.

These applications show that the so-called insoluble Prussian blues, either the chemical compound ferric ferrocyanide, or the commonly known insoluble Prussian blue, are more effective catalysts at high pressure operation than are the soluble Prussian blues. Thus when operating the combustion chamber containing the solid propellant at pressures between about 500 and 2000 p.s.i a higher burning rate, inches per second, is obtainable when using a given composition containing insoluble Prussian blue as the catalyst than is obtainable when using the same composition using soluble Prussian blue as the catalyst. The insoluble Prussian blue containing explosive compositions are diflicult to ignite at atmospheric pressures when the amount of catalyst present is less than about 6 weight percent. However, these compositions ignite readily when an elevated pressure is imposed on the combustion chamber prior to the application of the igniting means.

An application, Serial Number 288,549, now Patent No. 3,028,273, filed May 17, 1952, by Wayne A Proell, discloses that ammoniated insoluble Prussian blue is an effective catalyst for the combustion of ammonium nitrate or ammonium nitrate-oxidizable material mixtures. The ammoniated insoluble Prussian blue catalyst possesses the ignition characteristics of the soluble Prussian blue catalyst and the burning rate characteristics of the insoluble Prussian blue catalyst. When used in the mixture in amounts of about 3 to 4%, the ammoniated insoluble Prussian blue catalyzed mixture is hard to ignite and does not sustain combustion in an inert atmosphere. The ammoniated insoluble Prussian blue catalyst is produced by exposing an insoluble Prussian blue to the action of ammonia gas. The temperature of the reaction zone containing the insoluble Prussian blue and ammonia gas increases rapidly until a temperature of about 60 C. is reached; as the temperature increases, the rate of increase decreases until at about 60 C. a plateau is reached. As measured by temperature increase, the interaction of ammonia and the insoluble blue is believed to substantially stop when the temperature of the reaction zone reaches the plateau of about 60 C. The ammoniated insoluble Prussian blue has a strong odor of ammonia after being cooled to room temperature. An ammoniated insoluble Prussian blue of catalytic activity about equal to the odorous material which does not possess any appreciable ammonia odor can be obtained by maintaining the odorous material at a temperature of about 70 C. for several hours. The ammoniation of the insoluble Prussian blue does not change the physical appearance of the material and is noticeable principally in that the catalytic activity of the insoluble Prussian blue, particularly at low operating pressures, is markedly improved. By this treatment various catalytically active grades of insoluble Prussian blue can be converted to materials having about equal catalytic activity, i.e., the normal variation in catalytic activity of Prussion blue obtained from different manufacturers can be eliminated by this ammoniation procedure. The term ammoniated insoluble Prussian blue is intended to include both the ammonia-odorous material and the substantially odor-free material.

An application, Serial Number 287,623, now Patent No. 3,044,912 filed May 13, 1952, by Wayne A. Proell, discloses that alkali metal-iron cyanide and ammoniumiron cyanide are effective catalysts for sensitizing the ignition and combustion of ammonium nitrate-base ex-v plosives. Particularly elfective are potassium ferricyanide and ammonium ferricyanide. These iron cyanide catalysts are not as effective when used in compositions con-. taining oxygenated oxidizable materials as are the ironiron cyanide complexes, the soluble Prussian blues, the insoluble Prussian blues and the ammoniated insoluble Prussian blues. 1

The iron-type catalysts are preferred for use in the composition of this invention because of their low cost and ready availability. Further, they do not appreciably increase the heat sensitivity of the ammonium nitrate so that preparation of the shaped grain at temperatures approaching the melting point of ammonium nitrate can be used. Particularly advantageous is the fact that at the normal operating pressures of rocket motors and ATO units the insoluble Prussian blues and ammoniated insoluble Prussian blues give higher burning rates than do the other iron-type catalysts and the chromium-type catalysts. Still another advantage for the iron-type catalyst is the fact that the residue of the iron-type catalyst is a fine black powder producing substantially no smokiness in the combustion gases whereas the combustion residue of the chromium-type catalyst is a light, fluffy material which imparts smokiness to the combustion gases.

When using any one or a mixture of the iron-type catalysts defined above, between about 1 and 8 weight percent of catalyst is present in the explosive composition. Preferably, between about 2 and 4 weight percent of catalyst is used.

It is to be understood that the catalyst does consume some of the excess oxygen produced in the decomposition of the ammonium nitrate and this consumption of oxygen must be considered in determining the total oxygen demand of the explosive composition.

The explosive composition of this invention comprises essentially ammonium nitrate, a binder and a combustion catalyst. The ammonium nitrate is present in an amount of at least about 70 weight percent. An effective amount of combustion catalyst must be present and when using either a chromium-type catalyst or an iron-type catalyst, between about 1 and 8 Weight percent, preferably about 2 to 4 weight percent of catalyst is present in the ex. plosive composition. The amount of binder present in the explosive composition is between about 18 and 29 weight percent; preferably, the amount of binder should be adjusted to give a composition that is approximately stoichiometrically balanced with respect to oxygen.

The explosive composition of this invention can be prepared by several methods. A preferred procedure is set out below. The binder is heated until it has become a viscous fluid mass at a temperature on the order of C.

The desired amount of ammonium nitrate in a finely powdered condition is admixed with the desired amount of catalyst also in a finely powdered condition; this mixing is preferably carried out at ambient temperatures and precautions are taken to prevent the ammonium nitrate reaching a temperature approaching the melting point due to the friction of the mixing. The ammonium nitratecatalyst mixture is slowly added to the fluid binder while agitating the materials. The temperature of the three component mixture is preferably maintained below about 120 C. in order to minimize the possibilities of heat ignition of the composition. The materials are mixed until a smooth homogeneous paste has been obtained. This paste may be permitted to cool to ambient temperatures and then broken up into irregular pieces for uses such as blasting powder. Preferably, the pasty mass is formed into shapes of a configuration suitable for solid propellant purposes. The configurations are commonly called grains. The forming may be by introducing the pasty mass into suitable molds, either manually or mechanically by means of an injection molding technique, or preferably by extrusion. The composition of this invention flows fairly readily at temperatures above above 100 C. and becomes dimensionally stable at temperatures below about 90 C. This characteristic simplifies the problem of forming the grain because it eliminates the necessity for accelerated cooling of the mold or the extruded grain. The composition of the explosive of this invention has a very large advantage over conventional solid propellant compositions. It has been found that defective grains can be reworked alone or in admixture with fresh materials to produce satisfactory grains. The reworkability of rejects results in a substantial saving over conventional grains where rejects cannot be reworked.

It has been discovered that the extrudibility of the composition of this invention can be greatly improved without adversely affecting the characteristics of the shaped composition. It has been found that the pressure needed to extrude a tubular grain having an outside diameter of 0.25 inch could be decreased from about 2000 p.s.i. to about 1000 p.s.i. by adding between about 0.2 and 1 weight per cent of an alcohol, such as, heptanol, octanol, nonanol, steryl, etc.

The drawings show a particular application of this invention to an assisted take-off unit. The ATO unit illustrated is designed to be hung under the wing of an aircraft; normally at least two units, i.e., one under each wing, will be used. In FIGURE 1, the body of the unit is made up of a tubular member 11 which is closed at one end and which is provided with threads at the open end. Member 11 is provided with two loops, 12 and 13. These loops are used to hang the unit from a carrier, not shown, which is attached to the wing of the aircraft. This carrier makes it possible to jettison the unit after take-off. A somewhat funnel-shaped member 14 is attached to member 11 by engagement of the threads at the large open end of member 14 with the threads on member 11. Member 14 is provided with a nozzle 16 through which the decomposition products pass. The size of nozzle 16 determines in part the pressure maintained inside of the chamber formed by members 12 and 14.

The solid propellant fills the cylindrical portion of member 11. The solid propellant in this illustration consists of seven tubular grains, 17, 18, 19, 20, 21, 22 and 23; each having an CD. of about 3 inches and having a centrally located cylindrical opening 1 inch in diameter, the full length of the grain; the grains are approximately 30 inches long. The grains used herein consist essentially of 2% of ammoniated insoluble Prussian blue catalyst, 24% of binder and 74% of ammonium nitrate.

Each grain has the annular area at each end inhibited against burning by a coating of asphalt in order that the burning may take place on the cylindrical surfaces only. For some uses it is desirable to have a grain which burns cigarette fashion in which case the outer surface and one 10 end of the grain will be inhibited to prevent combustion. The inhibiting means may be asphalt, cellulose acetate, ethyl cellulose, acrylic plastics, etc.

Although a tubular grain is illustrated herein, the invention is not limited to such a grain. Any particular shape may be ultilized. Examples of other shapes are cylinder, cruciform, triform, hexaform, octaform and slab. 'In the case of perforated grains, the perforation may be circular or star-shaped with various numbers of points in the star. Furthermore, a single cylindrical grain having one or more longitudinal perforations may be utilized in some cases, instead of the multigrain unit shown.

The grains are held in longitudinal position and prevented by sliding back and forth in the combustion chamber by means of a wire grid 26. Wire grid 26 consists of a ring out to fit the threads of member 14 and provided with a grid work of metal wires that will resist the high temperature existing in the combustion chamber.

On one side of the conical portion of member 14 there is provided for the combustion chamber a safety venting means 28. Venting means 28 comprises a tubular member fastened to member 14, which tubular member has full access to the combustion chamber and is provided with a rupture disc, not shown. The rupture disc is of such construction that excess pressure in the combustion chamber will blow out the disc, whereby the pressure in the combustion chamber will be held below the point of serious damage to the unit.

An igniter means is positioned within member 14 so as to close off the nozzle 16. The igniter means consists of a container 31 filled with black powder, or some other easily ignited material, which can produce a large volume of gases at elevated pressure. A squib 32 for igniting the powder, is attached to the container 31 in communication with the powder contained therein. Electrical wires 33 connect a wire in the squib to the electrical system of the aircraft and a switch therein (the connections to the aircraft are not shown).

The ATO unit is assembled as follows: The grains are inserted into member 11. Venting means 28 are fastened to member 14. Igniter 31 is inserted through the large open end and fitted so as to close the nozzle, the wires '33 having first been passed through the nozzle 16. The wire grid 26 is screwed into the large open end of member 14. The assembled nozzle portion is then securely screwed onto member 11.

The assembled unit is then attached to the wing of the aircraft by loops 12 and 13; wires 33 are connected to the electrical operating assembly in the aircraft. When the pilot desires to obtain the assisted take-off, he throws the switch which causes the current to pass through wire 33 and to heat up the firing wire in squib 32, which in turn ignites the powder in the container 31.

The container is of sufiicient strength to withstand the initial pressure generated by the gases from the powder. The hot gases raise the pressure in the combustion chamber high enough to permit the grain to ignite. The combustion of the grain causes the pressure in the chamber to rise to a point which cannot be resisted by container 31. The container disintegrates and the pieces are discharged through nozzle 16. The total time from throwing the switch to full operation of the unit is on the order of less than 0.5 second.

As the gases pass out of the nozzle the reaction acts on the aircraft and adds its thrust to assist the aircrafts propeller; a marked increase is forward speed results and permits the aircraft to take off in a shorter space of time or it permits lifting a load heavier than could be airborne by the use of the propellers alone.

When using about 4% or more of the iron-type catalyst, the grain will ignite at relatively low pressures and no special precautions are necessary to maintain elevated pressure in the chamber until ignition occurs, as shown above. In this case, the igniter may be introduced into the combustion chamber by a means attached to the 1 l conical portion of member 14 (this procedure is conventionally used and is illustrated in U.S. 2,479,828) and no closure is placed on nozzle 16.;

The conventional placement of the igniter may be used with the lower catalyst content grains. However, it is necessary to use a much heavier powder charge in the igniter or, preferably, the nozzle is provided with a rupture disc, which is set to blow out at about 500 p.s.i. Other methods of igniting the grain can be readily devised.

While the invention has been illustrated by means of an assisted take-off operation, it must be understood that the solid propellant of this invention can also be used for other purposes. Some of these are air-to-air missiles, ground-to-ground missiles, blasting powder, etc. An important use of the invention lies in the production of gases at elevated pressures in a stationary or a portable system; discontinuous operation is readily obtained when using about 2% of catalyst as the composition can be extinguished readily by merely depressuring the combustion chamber.

An extremely important use of the composition of this invention lies in the field of propellent powder for small arms ammunition, artillery powder and so-called cannon powder. Small arms ammunition is intended to include cartridges for pistols and rifles and shells for shotguns. Artillery ammunition is intended to include the self-contained ammunition, i.e., a shell wherein the projectile and the casing that contains the powder and igniter are in one piece, much like a rifle cartridge. For very large caliber, artillery pieces such as 120 mm. antiaircarft guns and 6 inch or greater naval guns, separate ammunition is used, i.e., the projectile and the propelling powder are separate. Usually the powder is contained in special cloth bags. One of the most serious problems in artillery weapons is the extremely rapid wear of the bore, particularly when firing is at a continuous high rate. The commonly used propellant, Ballistite, has a flame temperature of about 5900 F., which temperature softens the barrel and permits the projectile to erode away the riding quite rapidly. Not only is the composition of this invention much cheaper than Ballistite, but also the much lower flame temperature of about 3900" F. permits a much longer useful life of the rifled barrel. Another desirable feature of this composition is that it is virtually smokeless.

The propellant for use in small arms is normally used in the form of short, solid thread-like filaments varying in lengthfrom about 0.1 to 0.2 inch. These grains are obtained by forcing the pasty powder through a multiple hole die to form filaments which may be between about 1 and mm. in diameter. These filaments are chilled by an air blast in order to form long threads of propellant. The threads are broken into short lengths and graded by a screening operation. The diameter of the filament-like grain controls the gas evolution rate when the grain is ignited. For some uses instead of a solid thread or spaghetti grain, a perforated macaroni-type grain may be used. This macroni-type grain is particularly useful for smaller caliber artillery ammunition. For separate ammunition use it has been found that grains which are hexagonal in external outline and are provided with longitudinal perforations are preferable because the hexagonal shape permits the formation of large multiple grains of a honeycomb structure, which grains can be readily fitted into a cloth bag of the required diameter for the particular gun. These perforated hexagonal grains may be as much as 1 or 2 inches in diameter and several inches long. The number of perforations in the hexagonal grain is dependent on the gas evolution rate desired.

The following information is presented to illustrate the preparation of the binder composition and the shaped explosive composition; the effectiveness of the explosive composition for gas generation; and the resistance of the shaped explosive composition to fissuring when subjected 12 to temperatures over the range of about -l00 F. to +170" P.

All of the test grains presented herein were made with a binder that had been prepared as follows:

The polymer was a commercial cellulose acetate purchased from Hercules and listed as LL-1 lacquer grade. This cellulose acetate analyzed between 55 and 56 weight percent of acetic acid and the viscosity of the standard acetone solution was between 2 and 4 centipoises at 25 C.

The modifier was 2,4-dinitrodiphenyl oxide.

The plasticizer was prepared by reacting ethylene glycol and diglycolic acid in a mol ratio of glycol-to-acid of 1.2. The glycol and acid were placed in a reactor which was provided with an agitator and a reflux condenser. A vacuum pump was connected to the condenser. The reactants were heated to about 150 C. Water formed in the polyesterification reaction was withdrawn and the reaction continued until substantially no water was being evolved. The total reaction time was about 4 hours. The polyesterification reaction product had the following physical properties at 25 C.: Specific gravity, 1.35; refractive index, 1.475; viscosity, 578 centistokes at F.

The ammonium nitrate used was technical grade and had a particle sizeRotap analysisas follows:

Mesh size: Wt. percent retained +35 Trace 35-60 5 6080 7 Dust 17 The catalyst was finely pulverized in a Mikro pulverizer in order to permit more uniform distribution with the ammonium nitrate.

The explosive composition was prepared in the following sequence of steps. The desired amounts of plasticizer and modifier were added together in an agitated vessel and the materials were heated to C. The materials were mixed at this temperature until a homogeneous viscous liquid had been obtained. The desired amount of polymer was added to the vessel and the materials maintained at a temperature of about 150 C. until a homogeneous viscous mass had been obtained. (The binder as prepared above was quite thermoplastic in nature and could be cooled to room temperature to give a tough, horny solid and then recoverted into a viscous fluid by heating to an elevated temperature.)

The molten binder was cooled to 120 C. and then a mixture of the required amounts of ammonium nitrate and catalyst were added to the container. The contents of the vessel were stirred while the temperature was maintained below approximately 120 C. until a uniformly mixed pasty mass had been obtained. This pasty mass was cooled to about 100 C. and then shaped into the desired configurations by various methods. The composition described above was somewhat plastic at a temperature of about 90 C. (195 F.) but quickly became rigid at temperatures below 90 C. and was quite dimensionally stable at 75 C. F.).

Cylinders of about 1 inch diameter and about 1.5 inches long were prepared by the use of a hand press. The required amount of material to make a dense cylinder was placed into a steel mold having a 1 inch inside diameter and about 50 pounds of pressure was applied on the material through a close-fitting plunger. The cylinders prepared in this way were dense and had a smooth, hard surface. These cylinders were quite strong and could stand a considerable amount of rough treatment.

Large size hollow grains were prepared for use in a miniature rocket motor. These grains as molded were 8 inches long, 2.75 inches in diameter and had a 1 inch longitudinal coaxial perforation. The 2.75 inch grain was machined to an outside diameter of 2.5 inches for use in the rocket motor. The composition machined readily on an ordinary lathe to give a grain of a smooth, very hard surface. This large perforated grain was prepared by the use of a steel mold which was provided with a 1 inch steel core. The desired amount of explosive composition was prepared and maintained at a temperature of 120 C.; by the use of an oven the mold was heated to 120 C. The required amount of material was manually placed into the mold and tamped into place with a wooden paddle. A steel disc 2.75 inches in diamter was then inserted into the open end of the mold and by means of a hydraulic piston, about 100 lbs. pressure of 70 C. (+158 F.). The glass-enclosed grain was then removed and held at ambient temperature about 25 C. for 1 hour. Then the glass-enclosed grain was buried in Dry Ice for 3 hours; Dry Ice temperature is -80 C. (112 F.) The glass-enclosed grain was removed and allowed to come to an embient temperature; the grain was removed from the glass bottles and inspected for cracks on the surface. (It has been noted that grains fail by cracks that appear on the surface of the grain. Failure by internal fissuring has not occurred in the grain configurations tested herein.)

The grain was cycled to failure or for eight cycles, whichever occurred first. Cycling tests indicate that passage of eight cycles is a sutficient indication that the grain was applied to the disc in order to compact the explosive 15 will cycle indefinitely. material. The mold and contents were allowed to cool The large perforated grains were tested as described gradually to about 50 C.; at this temperature the grain above except that instead of using glass bottles the grain was removed from the mold. The grain was permitted was protected by the use of a polyethylene bag. For the to cool gradually to room temperature and was then large grain it appears that successful completion of eight machined to a 2.5 inch outside diameter and was sawed cycles indicates satisfactory resistance to fissuring upon into 4 inch lengths. temperature change. It has been found that grains which For burning rate tests, grains about 6 inches long and successfully pass eight cycles on the 1 inch cylinder test .25 inch in diameter were prepared by extrusion. A labalso pass eight cycles on the large perforated grain test. oratory extrusion device was prepared. A chamber for The composition, burning rate and cycling test results the explosive was adapted to be maintained at a temare given in the table for five grains. For purposes of perature of between and C. A hydraulic piscomparison, grain I was prepared without a catalyst. ton was used to force the explosive from the chamber Since this grain could not be ignited no cycling test was through an 0.25 inch die to give a grain of the proper carried out. The cylindrical grains that had passed the diameter. The hydraulic piston could develop pressures cycling test were tested for internal fissuring by burning up to 2000 p.s.i. It was found that by using this device 30 at ambient temperature and pressure; the grains burned 30 inch strands could be prepared readily. uniformly and smoothly. This smooth burning indicated The burning rate in inches per second of various comno fissuring as fissures cause uneven burning, i.e., sudden positions were determined at elevated pressures by the increases in gas evolution result when a fissure is reached. use of a Crawford bomb. This device permits measuring The large grain No. V was tested in the miniature motor the burning rate of a strand of material at a constant and burned smoothly.

Table Binder Composition 1 Explosive Composition 1 Burning Cycles Rate, 'Grain N0. Catalyst Passed in./sec., Comment CA Ester DNDPO Binder Nitrate 1.000 Type Percent p.s.L

20.0 40.0 40.0 25.2 74.8 None None Would not ignite. 25.0 37. 5 37. 5 24. 0 72. 0 Di- 2. 0 8 0. Cylinder Cycling Test. 20.0 40.0 40.0 24.7 73.3 so luble Priissian 2.0 8 0.130 Do.

19.8 40.1 40.1 24.2 71.8 4.0 8 0.140 Do. 20.0 40.0 40.0 24.7 73.3 Ammoniated S0111 2.0 8 0.131 Large grain held '1' days at; F.

ble Prussian Blue. without deterioration.

1 Wt. percent.

pressure in the combustion chamber. The bomb is brought to thedesired pressure by the use of cylinder nitrogen and the strand is ignited by means of a hot wire. Duplicate runs were made in order to determine the reproducibility of the burning rates. Although there is an appreciable change in burning rate with increase in pressure, normally burning rates are reported at 1000 p.s.i. operating pressure since this is about the operating pressure of ATO units.

The resistance of the particular composition to fissuring on temperature change was determined by a laboratory method. No standard test has as yet been established by testing laboratories and the test described below was developed by the applicants and is believed to be a good indication of the cycling resistance of the particular composition.

A preliminary screening procedure utilized solid cylinders of 1 inch diameter and 1.5 inch length. The grain was placed in a glass bottle containing a small amount of drying agent; and drying agent prevents the condensation of water on the grain at Dry Ice temperatures. This bottle was enclosed in a second glass 'bottle. The glassenclosed grain was placed in a thermostatically controlled oven and maintained for 4 hours at an oven temperature In order to simulate large scale operation, a miniature rocket motor was constructed. This motor consisted essentially of a cylinder closed at one end and threaded at the open end. The straight side of the cylinder was about 8 inches along and the cylinder had an internal diameter of about 3 inches. A funnel-shaped portion provided with an opening for the attachment of a nozzle and provided with threads at the larger end was threaded onto the cylindrical casing to complete the combustion chamber of the motor. Various sized orifices were provided in order to permit the operation of the motor at difi'erent combustion chamber pressures. These orifices varied from 0.17 to 0.24 inch in diameter. By varying the orifice size, the combustion chamber pressure could be varied from about 700 to about 2000 p.s.i.

In order to reduce the amount of explosive material needed per motor test, a perforated cylindrical aluminum slug was used to take up about half the longitudinal volume of the motor. Thus in operation the motor contained the slug and a 2.5 inch diameter perforated grain 4 inches long.

The grain was ignited by a black powder mixture, which mixture was in turn ignited by means of an electrical squib.

It was found that satisfactory ignition could be obtained by using 25 g. of the following mixture: sparkler powder, g.; FFG gun powder, 7.5 g.; and FFFG powder, 7.5 g. This mixture was placed at the nozzle end of the funnelshaped member and was held in place by means of a paper disc pressed firmly against the sloping sides of the memher. The motor was assembled by inserting into the casing first the aluminum slug and then the grain to be tested. The test grain was inhibited on both annular ends by coating the annular area with asphalt. This inhibiting of the annuli results in the burning of the cylindrical surfaces only. The nozzle end complete with powder igniter was then screwed to the casing. The electrical suib was then inserted through the nozzle opening until it contacted the powder mixture. This method of arming the motor is particularly desirable because the motor is essentially inert until a few seconds before the test run is fired. It has been found that this method of ignition gives ignition delays between about 100 and 500 milliseconds.

On a motor test of grain V a smooth burning was obtained at a combustion chamber pressure of 1000 psi. when using a nozzle of 0.22 inch diameter. This grain burned with a sharp increase in chamber pressure to 1000 p.s.i. and then burned to completion at a plateau of about 1000 p.s.i.; substantially no drop in chamber pressure was noticed near the end of the burning period. The calculated specific impulse for this grain at a chamber pressure of about 1000 psi was approximately 200 seconds.

In order to determine the nature of the burning, the combustion of several grains in the motor test was stopped by depressuring of the motor. The partially burned grains had smooth surfaces, indicating substantially uniform burning over the entire uninhibited surface. There was a complete absence of the so-called wormholes which indicate burning through transverse flaws in the body of the grain.

We claim:

1. An explosive composition which comprises essentially (1) at least about 70 weight percent of ammonium nitrate, (2) an effective amount of a combustion catalyst, and (3) between about 18 and 29 weight percent of a binder, which binder comprises essentially (A) between about 18 and 40 weight percent of cellulose acetate which analyzes between about 51 and 57 weight percent of acetic acid; (B) between about 20 and 60 weight percent of the polyester condensation product of (i) at least one dihydric alcohol selected from the class consisting of ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, n-butylene glycol and poly n-butylene glycol, which polyglycols have a molecular weight of less than about 400, and (ii) at least one acid selected from the class consisting of alkyl dicarboxylic acids and alkyl oxydicarboxylic acids, which acids contain between 2 and 6 carbon atoms, and wherein the mol ratio of said alcohol to said acid is between about 1.02 and 1.3; and (C) between 20 and 60 weight percent of a modifier selected from the class consisting of mononitrodiphenyl, di-

nitrodiphenyl, mixtures of mononitrodiphenyl and dinitrodiphenyl, mixtures of the foregoing with trinitrodiphenyl, mononitrodiphenyl oxide, dinitrodiphenyl oxide, mixtures of mononitrodiphenyl oxide, and dinitrodiphenyl oxide and mixtures of the foregoing oxides with trinitrodiphenyl oxide, in which trinitro compound-containing mixtures there is an average if less than about 2.5 nitro groups per molecule and essentially not more than two nitro groups are present on any benzene nucleus.

2. The composition of claim 1 wherein said combustion catalyst is present in an amount between about 1 and i 8 weight percent and said catalyst consists of at least one member of the class consisting of iron-iron cyanide complexes, soluble Prussian blue, insoluble Prussian blue, ammoniated insoluble Prussian blue, ammonium iron cyanide and alkali-metal iron cyanide and mixtures thereof.

3. The composition of claim 1 wherein said catalyst is ammoniated insoluble Prussian blue and wherein said catalyst is present in an amount between about 1 and 8 weight percent.

4. The composition of claim 1 wherein said cellulose acetate analyzes between about 54 and 56 weight percent of acetic acid.

5. The composition of claim 1 wherein said alcohol is v ethylene glycol.

6. The composition of claim 1 wherein said acid is diglycolic acid.

7. The composition of claim 1 wherein said modifier is dinitrodiphenyl oxide.

8. The composition of claim 7 wherein said dinitrodiphenyl oxide is the 2,4-isomer.

9. An explosive composition which comprises essentially (1) at least about weight percent of ammonium nitrate, (2) between about 2 and 4 weight percent of a combustion catalyst selected from the class consisting of iron-iron cyanide complexes, soluble Prussian blue, insoluble Prussian blue, ammoniated insoluble Prussian blue, ammonium iron cyanide, alkali-metal iron cyanide and mixtures thereof, (3) between about 18 and 29 weight percent of a binder, which binder comprises es-.

sentially (A) between about 18 and 25 weight percent of cellulose acetate which analyzes between about 54 and 56 Weight percent of acetic acid, (B) between about 25 and 45 weight percent of the polyester condensation product of (i) at least one dihydric alcohol selected from the class consisting of ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, n-butylene glycol and poly n-butylene glycol, which polyglycols have a molecular weight of less than about 400, and (ii) at least one acid selected from the class consisting of alkyl dicarboxylic acids and alkyl oxydicarboxylic acids, which acids contain between 2 and 6 carbon atoms, and wherein the mol ratio of said alcohol to said acid is between about 1.15 and 1.25, and (C) between about 25 and 45 weight percent of a modifier selected from the class consisting of mononitrodiphenyl, dinitrodiphenyl, mixtures of mononitrodiphenyl and dinitrodipheyl, mixtures of the foregoing References Cited by the Examiner UNITED STATES PATENTS 2,434,872 1/ 48 Taylor et al. 2,568,080 9/51 McGahey 102-38 2,592,623 4/52 Turnbull 10238 CARL D. QUARFORTH, Primary Examiner.

WILLIAM G. WILES, Examiner. 

1. AN EXPLOSIVE COMPOSITION WHICH COMPRISES ESSENTIALLY (1) AT LEAST ABOUT 70 WEIGHT PERCENT OF AMMONIUM NITRATE, (2) AN EFFECTIVE AMOUNT OF A COMBUSTION CATALYST, AND (3) BETWEEN ABOUT 18 AND 29 WEIGHT PERCENT OF A BINDER, WHICH BINDER COMPRISES ESSENTIALLY (A) BETWEEN ABOUT 18 AND 40 WEIGHT PERCENT OF CELLULOSE ACETATE WHICH ANALYZES BETWEEN ABOUT 51 AND 57 WEIGHT PERCENT OF ACETIC ACID; (B) BETWEEN ABOUT 20 AND 60 WEIGHT PERCENT OF THE POLYESTER CONDENSATION PRODUCT OF (I) AT LEAST ONE DIHYDRIC POLYESTER CONDENSATION PRODUCT OF (I) AT LEAST ONE DIHYDRIC ALCOHOL SELECTED FROM THE CLASS CONSISTING OF ETHYLENE GLYCOL, POLYETHYLENE GLYCOL, PROPYLENE GLYCOL, POLYPROPYLENE GLYCOL, N-BUTYLENE GLYCOL AND POLY N-BUTYLENE GLYCOL, WHICH POLYGLYCOLS HAVING A MOLECULAR WEIGHT OF LESS THAN ABOUT 400, AND (II) AT LEAST ONE ACID SELECTED FROM THE CLASS CONSISTING OF ALKYL DICARBOXYLIC ACIDS AND ALKYL OXYDICARBOXYLIC ACIDS, WHICH ACIDS CONTAIN BETWEEN 2 AND 6 CARBON ATOMS, AND WHEREIN THE MOL RATIO OF SAID ALCOHOL TO SAID ACID IS BETWEEN ABOUT 1.02 AND 1.3; AND (C) BETWEEN 20 AND 60 WEIGHT PERCENT OF A MODIFIER SELECTED FROM THE CLASS CONSISTING OF MONONITRODIPHENYL, DINITRODIPHENYL, MIXTURES OF MONONITRODIPHENYL AND DINITRODIPHENYL, MIXTURES OF THE FOREGOING WITH TRINITRODIPHENYL, MONONITRODIPHENYL OXIDE, DINITRODIPHENYL OXIDE, MIXTURES OF MONONITRODIPHENYL OXIDE, AND DIMITRODIPHENYL OXIDE AND MIXTURES OF THE FOREGOING OXIDES WITH TRINITRODIPHENYL OXIDE, IN WHICH TRINITRO COMPOUND-CONTAINING MIXTURES THERE IS AN AVERAGE IF LESS THAN ABOUT 2.5 NITRO GROUPS PER MOLECULE AND ESSTENTIALLY NOT MORE THAN TWO NITRO GROUPS ARE PRESENT ON ANY BENZENE NUCLEUS. 